Separating and recovering only the objective hydrocarbon gas from a mixed gas containing hydrocarbons has been known in the art.
An example of a hydrocarbon gas to be separated and recovered is 1,3-butadiene. 1,3-Butadiene is a useful compound, for example, as a starting material for the production of a synthetic rubber, and also an intermediate of large number of compounds. Commonly, 1,3-butadiene is produced by naphtha cracking or dehydrogenation of butenes. According to these productions methods, 1,3-butadiene is obtained as one component of a mixed gas. Therefore, it is necessary to selectively separate and recover 1,3-butadiene from the gas mixture. Examples of the main component having 4 carbon atoms in the product include 1,3-butadiene, isobutene, 1-butene, 2-butene, normal butane, and isobutane. Since these compounds have the same carbon number and the similar boiling point, it is difficult to separate them by an industrially employed distillation method.
An example of one of other separating methods is an extractive distillation method. This method is an absorption method using a polar solvent, and thus too much energy is used to separate 1,3-butadiene from the polar solvent. Therefore, separation by an adsorption method is desired as a method for separating and recovering 1,3-butadiene in an energy-saving manner.
However, a conventional porous material (Patent Literature 1) requires separating in a multi-stage because of poor separation performance of 1,3-butadiene, thus failing to avoid upsizing of a separation apparatus.
There has been developed, as an adsorption material capable of achieving more excellent separation performance than that of a conventional porous material, a porous metal complex which causes dynamic structural change due to external stimulation (Non-Patent Literatures 1 and 2). When using this porous material as a gas adsorption material, it has been observed that there is a particular characteristic in which gas is not adsorbed below a certain pressure, but gas adsorption occurs above a certain pressure. In addition, it has been observed that there is a characteristic in which an adsorption initiation pressure varies depending on the type of a gas subjected to adsorption.
Applying this porous material to, for example, an adsorption material in a gas separating apparatus of a pressure swing adsorption system enables gas separation with excellent efficiency. It also enables narrowing of a swing width of the pressure, which leads to the energy saving. Because of its contribution to miniaturization of the gas separating apparatus, it enables not only the enhancement of cost competitiveness in the case of selling a highly pure gas as the product, but also the reduction in cost required for equipment which needs a highly pure gas even when the highly pure gas is captively consumed inside a factory, thus eventually having the effect of reducing production cost of the final product.
There are disclosed metal complexes [Zn(R-ip)(bpe)] (R═H, Me, NO2, I) composed of zinc ions, various isophthalic acid derivatives, and 1,2-di(4-pyridyl)ethylene (Patent Literature 2, and Non-Patent Literature 3). Although the study focused on adsorption and separation of a gas mixture containing hydrocarbons having 2 carbon atoms, no study have carried out in terms of adsorption and separation of a gas mixture containing hydrocarbons having 4 carbon atoms, which includes 1,3-butadiene.